/* -*- P4_16 -*- */
#include <core.p4>
#include <v1model.p4>

const bit<16> TYPE_IPV4 = 0x800;

/*************************************************************************
*********************** H E A D E R S  ***********************************
*************************************************************************/
typedef bit<9>  egressSpec_t;
typedef bit<48> macAddr_t;
typedef bit<32> ip4Addr_t;

header ethernet_t {
    bit<48> dstAddr;
    bit<48> srcAddr;
    bit<16> etherType;
}

header ipv4_t {
    bit<4>  version;
    bit<4>  ihl;
    bit<8>  diffserv;
    bit<16> totalLen;
    bit<16> identification;
    bit<3>  flags;
    bit<13> fragOffset;
    bit<8>  ttl;
    bit<8>  protocol;
    bit<16> hdrChecksum;
    ip4Addr_t srcAddr;
    ip4Addr_t dstAddr;
}

header tcp_t {
    bit<16> srcPort;
    bit<16> dstPort;
    bit<32> seqNo;
    bit<32> ackNo;
    bit<4>  dataOffset;
    bit<3>  res;
    bit<3>  ecn;
    bit<6>  ctrl;
    bit<16> window;
    bit<16> checksum;
    bit<16> urgentPtr;
}

struct metadata {
    bit<14> ecmp_select;
    bit<1>  ecmp_valid;
}

struct headers {
    ethernet_t ethernet;
    ipv4_t     ipv4;
    tcp_t      tcp;
}

/*************************************************************************
*********************** P A R S E R  ***********************************
*************************************************************************/
parser MyParser(packet_in packet,
                out headers hdr,
                inout metadata meta,
                inout standard_metadata_t standard_metadata) {

    state start {
        transition parse_ethernet;
    }

    state parse_ethernet {
        packet.extract(hdr.ethernet);
        transition select(hdr.ethernet.etherType) {
            TYPE_IPV4: parse_ipv4;
            default: accept;
        }
    }

    state parse_ipv4 {
        packet.extract(hdr.ipv4);
        transition select(hdr.ipv4.protocol) {
            6: parse_tcp;
            default: accept;
        }
    }

    state parse_tcp {
        packet.extract(hdr.tcp);
        transition accept;
    }
}

/*************************************************************************
************   C H E C K S U M    V E R I F I C A T I O N   *************
*************************************************************************/
control MyVerifyChecksum(inout headers hdr, inout metadata meta) {
    apply { }
}

/*************************************************************************
**************  I N G R E S S   P R O C E S S I N G   *******************
*************************************************************************/
control MyIngress(inout headers hdr,
                  inout metadata meta,
                  inout standard_metadata_t standard_metadata) {

    action drop() {
        mark_to_drop(standard_metadata);
    }

    // ECMP selection action
    action set_ecmp_select(bit<16> ecmp_base, bit<32> ecmp_count) {
        bit<32> src_ip = hdr.ipv4.srcAddr;
        bit<32> dst_ip = hdr.ipv4.dstAddr;
        bit<8>  proto  = hdr.ipv4.protocol;
        bit<16> sport  = hdr.tcp.srcPort;
        bit<16> dport  = hdr.tcp.dstPort;

        hash(meta.ecmp_select,
             HashAlgorithm.crc16,
             ecmp_base,
             {src_ip, dst_ip, proto, sport, dport},
             ecmp_count);
        meta.ecmp_valid = 1;
    }

    // ECMP group table - matches VIP addresses
    table ecmp_group {
        key = {
            hdr.ipv4.dstAddr: lpm;
        }
        actions = {
            set_ecmp_select;
            drop;
        }
        size = 1024;
        default_action = drop();
    }

    // ECMP next hop table
    action set_nhop(macAddr_t nhop_dmac, ip4Addr_t nhop_ipv4, egressSpec_t port) {
        // Rewrite MAC addresses
        hdr.ethernet.srcAddr = hdr.ethernet.dstAddr;
        hdr.ethernet.dstAddr = nhop_dmac;

        // Update IPv4 destination for VIP traffic
        hdr.ipv4.dstAddr = nhop_ipv4;

        // Set egress port and decrement TTL
        standard_metadata.egress_spec = port;
        hdr.ipv4.ttl = hdr.ipv4.ttl - 1;
    }

    table ecmp_nhop {
        key = {
            meta.ecmp_select: exact;
        }
        actions = {
            set_nhop;
            drop;
        }
        size = 1024;
        default_action = drop();
    }

    // Regular IPv4 forwarding
    action ipv4_forward(macAddr_t dstAddr, egressSpec_t port) {
        standard_metadata.egress_spec = port;
        hdr.ethernet.srcAddr = hdr.ethernet.dstAddr;
        hdr.ethernet.dstAddr = dstAddr;
        hdr.ipv4.ttl = hdr.ipv4.ttl - 1;
    }

    table ipv4_lpm {
        key = {
            hdr.ipv4.dstAddr: lpm;
        }
        actions = {
            ipv4_forward;
            drop;
        }
        size = 1024;
        default_action = drop();
    }

    apply {
        if (hdr.ipv4.isValid()) {
            if (hdr.ipv4.ttl == 0) {
                drop();
                return;
            }

            // First check if this is ECMP traffic
            meta.ecmp_valid = 0;
            ecmp_group.apply();

            if (meta.ecmp_valid == 1) {
                // Handle ECMP traffic
                ecmp_nhop.apply();
            } else {
                // Handle regular IPv4 forwarding
                ipv4_lpm.apply();
            }
        }
    }
}

/*************************************************************************
****************  E G R E S S   P R O C E S S I N G   *******************
*************************************************************************/
control MyEgress(inout headers hdr,
                 inout metadata meta,
                 inout standard_metadata_t standard_metadata) {
    apply { }
}

/*************************************************************************
*************   C H E C K S U M    C O M P U T A T I O N   **************
*************************************************************************/
control MyComputeChecksum(inout headers hdr, inout metadata meta) {
    apply {
        update_checksum(
            hdr.ipv4.isValid(),
            { hdr.ipv4.version,
              hdr.ipv4.ihl,
              hdr.ipv4.diffserv,
              hdr.ipv4.totalLen,
              hdr.ipv4.identification,
              hdr.ipv4.flags,
              hdr.ipv4.fragOffset,
              hdr.ipv4.ttl,
              hdr.ipv4.protocol,
              hdr.ipv4.srcAddr,
              hdr.ipv4.dstAddr },
            hdr.ipv4.hdrChecksum,
            HashAlgorithm.csum16);
    }
}

/*************************************************************************
***********************  D E P A R S E R  *******************************
*************************************************************************/
control MyDeparser(packet_out packet, in headers hdr) {
    apply {
        packet.emit(hdr.ethernet);
        packet.emit(hdr.ipv4);
        packet.emit(hdr.tcp);
    }
}

/*************************************************************************
***********************  S W I T C H  *******************************
*************************************************************************/
V1Switch(
MyParser(),
MyVerifyChecksum(),
MyIngress(),
MyEgress(),
MyComputeChecksum(),
MyDeparser()
) main;
